In cooperative with Dr. Cook and his pre- and postdoctoral coworkers, our general synthesis of di- and polycyclic ring systems composed of five-membered rings has been studied. Our earlier hypothetical interpretation of the reaction sequence involved in the formation of these compounds has been proved experimentally. The unusual reactivity of some of these systems has been explained, and one of them has been utilized for a new synthesis of the sesquiterpene modhephene. The complete structure and stereochemistry of the antibiotics chrysomycin A and B have been elucidated, in cooperation with Dr. Highet and the group of FCRC. The antibiotic (mixture of 86% A and 14% B) has good antileukemic action on intraperitoneal administration to rats, and is tolerated in high doses. It has been established in cooperation with Dr. Kirk that the chloromorphine obtained from morphine in dilute HCl with potassium iodate is indeed 1-chloromorphine, since it differs from authentic 2-chloromorphine, the alternative product which would actually have been expected on general principles. A plausible explanation for the anomalous formation of 1-chloromorphine has been given.